The present invention relates to a plate exchange apparatus for a printing press, which exchanges an old plate gripped by a plate lockup device and mounted on the circumferential surface of a plate cylinder for a new plate prepared outside the appearance.
A gap having a length almost equal to the overall length of a plate cylinder is formed in the circumferential surface of the plate cylinder for a printing press. A plate lockup apparatus consisting of a leading-side lockup device for gripping the leading end of a plate and a trailing-side lockup device for gripping the trailing end of the plate, the leading end of the plate being gripped by the leading-side lockup device while the plate is wound around the circumferential surface of the plate cylinder, is fixed on the bottom surface of the gap to extend in the axial direction of the plate cylinder. Each of the conventional leading- and trailing-side lockup devices comprises an elongated lockup table extending in the axial direction of the plate cylinder, a plurality of gripper plates, swingably supported at an edge portion of this lockup table by a plurality of bolts, for gripping or releasing the plate with or from the lockup table by being opened or closed as they swing, and a plurality of cams which can be respectively engaged with notches at the edges of the gripper plates. The plurality of cams are aligned along a pivotal cam shaft. A plurality of compression coil springs are interposed between the lockup table and the gripper plates to bias the gripper plates in an open direction.
With the above arrangement, in order to grip a plate, when the cam shaft is pivoted, the gripper plates are released upon disengagement from the cams and are opened by the elastic forces of the compression coil springs. An end of the plate is inserted between the gripper plates and the corresponding lockup table. When the cam shaft is pivoted in the direction opposite to the direction described above, the gripper plates are pivoted against the elastic forces of the compression coil springs by the behavior of the cams and closed, thereby gripping the end of the plate.
However, in the conventional plate lockup apparatus as described above, the cam shaft must be manually rotated in order to open and close the plate gripper surfaces, as described above. Therefore, the number of processing steps is increased to degrade the operability, resulting in need for much labor, and the preparation time is prolonged to degrade the operating efficiency of the printing press.
Hence, the present applicant developed and proposed a plate exchange apparatus in which a plate holding unit holding a new plate is provided between the printing press units, an old plate removed from the plate cylinder is discharged to and held in the plate holding unit, and the new plate is discharged from the plate holding unit and mounted on the plate cylinder. In this case, however, in order to correctly discharge the old plate removed from the plate cylinder into the plate holding unit and to correctly grip the new plate with the plate lockup device of the plate cylinder, the relative positions of the distal end of the plate holding unit which is swung for plate discharge and plate supply and the plate lockup device must be constantly correctly maintained.